Inorg. Chem. 2005, 44, 673−676
A Cyclic Hexamer of Silver Trifluoroacetate Supported by Four Triphenylphosphine Sulfide Template Molecules Bratislav Djordjevic, Oliver Schuster, and Hubert Schmidbaur* Department Chemie, Technische UniVersita¨t Mu¨nchen, Lichtenbergstrasse 4, 85747 Garching, Germany Received August 30, 2004
Crystallization of silver trifluoroacetate from chloroform solutions containing triphenylphosphine sulfide affords a trigonal and a monoclinic form of a 6:4 complex {[CF3C(O)OAg]6(Ph3PS)4} of C2 symmetry with different amounts of chloroform in the crystals. With the Ph3PS components as template molecules, the CF3C(O)OAg units are assembled to form a 6-membered metallacycle codetermined by metallophilic bonding and enclosed by a 24membered ring [AgOCO]6. A complex of the type [LAgOC(O)CF3]2, with L representing the isocyanide ligand pTolSO2CH2NC, has been shown to have a conventional bicyclic structure with three-coordinate silver atoms engaged in transannular metallophilic interactions.
Introduction Silver(I) carboxylates [AgOC(O)R]n with no auxiliary donor ligands have been shown to form oligomers with a variety of structural motifs including mainly dimers with flat eight-membered rings A1-3 or tetramers with folded 16membered rings B,4 the geometry of which is clearly codetermined by metallophilic bonding between the linearly two-coordinate metal atoms (Chart 1). Because of this low degree of aggregation, silver carboxylates with small nonpolarizable substituents (such as perfluoroalkyl -CnF2n+1) are volatile in a vacuum and can be employed as sources for the chemical vapor deposition of silver metal.5-8 With donor ligands L, the ring systems of 1:1 complexes [(L)AgOC(O)R]n and 1:2 complexes [(L)2AgOC(O)R]n can * Author to whom correspondence should be addressed. E-mail:
[email protected]. (1) Griffin, R. G.; Ellett, J. D.; Mehring, M.; Bullitt, J. G.; Waugh, J. S. J. Chem. Phys. 1972, 57, 2147. (2) Blakeslee, A. E.; Hoard, J. L. J. Am. Chem. Soc. 1956, 78, 3029. (3) Paramonov, S. E.; Mychlo, E. V.; Troyanov, S. I.; Kuz’mina, N. P. Zh. Neorg. Khim. 2000, 45, 2003. (4) Michaelides, A.; Kiritsis, V.; Skoulika, S.; Aubry, A. Angew. Chem., Int. Ed. Engl. 1993, 32, 1495. (5) Kodas, T. T.; Hampden-Smith, M. J. The Chemistry of Metal CVD; VCH: Weinheim, Germany, 1994; p 305. (6) Schmidt, H.; Shen, Y.; Leschke, M.; Haase, T.; Kohse-Ho¨nighaus, K.; Lang, H. J. Organomet. Chem. 2003, 669, 25. (7) (a) Edwards, D. A.; Mahon, M. F.; Molloy, K. C.; Ogrodnik, V. J. Chem. Mater. 2003, 13, 563. (b) Edwards, D. A.; Harker, R. M.; Mahon, M. F.; Molloy, K. C. Inorg. Chim. Acta 2002, 328, 134. (8) (a) Szlyk, E.; Szymanska, I.; Surdykowski, A.; Glowiak, T.; Woitczak, A.; Golinski, A. Dalton Trans. 2003, 3404. (b) Szlyk, E.; Piszczek, P.; Grodzicki, A.; Chaberski, M.; Golinski, A.; Szatkowski, J.; Blaszczyk, T. Chem. Vap. Deposition 2001, 7, 111.
10.1021/ic048795o CCC: $30.25 Published on Web 01/05/2005
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remain intact with the coordination number (CN) of the metal atoms increasing to 3 or 4, preserving metallophilic bonding as in C8,9 or losing the Ag---Ag contacts as in D (Chart 1).10 The literature is particularly rich in examples with L ) tertiary phosphines or arsines.5-17 It should be noted that the structural chemistry of the silver carboxylates is entirely different from that of the corresponding gold carboxylates, where complexes of the type [(L)AuOC(O)R] are generally monomers with the gold atoms linearly two-coordinate with complementary aurophilic bonding in a T-shaped geometry for small ligands L.18-23 Only (9) Paramonov, S. E.; Kuz’mina, N. P.; Troyanov, S. I. Polyhedron 2003, 22, 837. (10) Blues, E. T.; Drew, M. G. B.; Femi-Onadeko, B. Acta Crystallogr. 1977, B33, 3965. (11) Ro¨mbke, P.; Schier, A.; Schmidbaur, H.; Cronje, S.; Raubenheimer, H. Inorg. Chim. Acta 2004, 357, 235. (12) Van der Ploeg, A. F. M. J.; van Koten, G. Inorg. Chim. Acta 1981, 51, 225. (13) Chen, X.-M.; Mak, T. C. W. Polyhedron 1991, 10, 1723. (14) Hor, T. S. A.; Neo, S. P.; Tan, C. S.; Mak, T. C. W.; Leung, K. W. P.; Wang, R. J. Inorg. Chem. 1992, 31, 4510. (15) Neo, S. P.; Zhou, Z. Y.; Mak, T. C. W.; Hor, T. S. A. Inorg. Chem. 1995, 34, 520. (16) Edwards, D. A., Harker, R. M., Mahon, M. F., Molloy, K. C. Inorg. Chim. Acta 2002, 328, 134. (17) Che, C.-M.; Tse, M.-C.; Chan, M. C. W.; Cheung, K.-K.; Philips, D. L.; Leung, K.-H. J. Am. Chem. Soc. 2000, 122, 2464. (18) Nichols, D. I.; Charleston, A. S. J. Chem. Soc. A 1969, 2581. (19) (a) Jones, P. G. Acta Crystallogr., C 1985, 41, 905. (b) Jones, P. G.; Schelbach, R. J. Chem. Soc., Chem. Commun. 1988, 1338. (c) Jones, P. G.; Schelbach, R. Inorg. Chim. Acta 1991, 182, 239. (20) Fackler, J. P., Jr.; Khan, M. N. I.; King, C.; Staples, R. J.; Winpenny, R. E. P. Organometallics 1991, 10, 2178. (21) Baukova, T. V.; Kuz’mina, L. G.; Dvortsova, N. V. Zh. Neorg. Khim. 1992, 1497.
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Djordjevic et al. Chart 1
large ligands L may prevent the close approach necessary for bonding Au---Au contacts. Results An illustrative example for the standard behavior of the 1:1 complexes with an auxiliary ligand taken from the isocyanide series is presented here as a reference. The reaction between silver(I) trifluoroacetate and p-tolylsulfonylmethyl isocyanide (in chloroform) affords high yields of a colorless product {(pTolSO2CH2NC)Ag[OC(O)CF3]}2 (1). The structure of type C shown in Figure 1 approaches C2
Figure 1. Molecular structure of [pTolSO2CH2NCAgOC(O)CF3]2 (1) (ORTEP, 50% probability ellipsoids, hydrogen atoms omitted). The structure approaches C2 symmetry, the virtual 2-fold axis passing through the midpoint of the lines connecting the atoms Ag1 with Ag2 and N1 with N2. Bond distances and angles show no anomalies.
symmetry quite closely and features a metallophilic Ag---Ag contact of 3.0213(4) Å between silver atoms which are in a planar three-coordinate configuration. By contrast, the reaction of AgOC(O)CF3 with triphenylphosphine sulfide, also in a 1:1 molar ratio, gives a colorless 3:2 adduct of the components which crystallizes (22) Sladek, A.; Schneider, W.; Angermaier, K.; Bauer, A.; Schmidbaur, H. Z. Naturforsch., B 1996, 51, 765. (23) Preisenberger, M.; Schier, A.; Schmidbaur, H. Inorg. Chem. 1999, 38, 5870.
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from chloroform as pentane vapor is allowed to diffuse into solution. With only slight variations of the experimental conditions, which presently cannot really be specified, crops of crystals were obtained which contained various amounts of two crystalline phases which could be identified as different solvates containing the same hexanuclear species of the formula {(Ph3PS)4‚[AgOC(O)CF3]6} (2). Vacuumdried solvent-free samples (54% yield, mp 167 °C dec) have been characterized by elemental analysis and NMR spectroscopy. Only one set of 1H and 13C resonances and a 31P singlet (δ 46.8 ppm) were obtained for the four Ph3PS ligands, while the equivalence of the six CF3CO2 units was demonstrated by a 19F singlet (δ -73.4 ppm). Crystals of compound 2 are either trigonal (with a huge unit cell, Z ) 18) or monoclinic (Z ) 8), with space groups R3c and C2/c, respectively. In both phases, which differ only in their ill-defined contents of solvent molecules, complex 2 has crystallographically imposed C2 symmetry. The geometries are very similar, and therefore, only the structure of the molecules in the trigonal form is presented and discussed in detail here. The structure is best described as an extension of the series started in formulas A and B: Following an 8- and a 16membered ring, a 24-membered ring assembled of six silver atoms and six carboxylate OCO units is discernible, and in this macrocycle the six silver atoms are connected via metallophilic (argentophilic) bonding to give a 6-membered metallacycle in a twisted boat conformation (Figures 2 and 3). The average Ag---Ag contact is 3.020 Å. Six cornersharing five-membered rings CO2Ag2 are annelated to the metallacycle, two roughly in the best plane defined by the silver atoms, two above, and two below. Two pairs of triphenylphosphine sulfide molecules occupy symmetrical positions relative to the 2-fold axis above and below the macrocycle. Their sulfur atoms cap triangles of silver atoms (S1 for Ag2,Ag1,Ag3* and S2 for Ag1,Ag2, Ag3), providing each silver atom with two Ag-S contacts in addition to its two Ag-O contacts (Figure 4). The silver atoms thus become four-coordinate (AgO2S2) in a quasi-
A Cyclic Hexamer of SilWer Trifluoroacetate
Figure 2. Hexanuclear subunit (CF3CO2Ag)6 of the complex [(Ph3PS)4‚ (CF3CO2Ag)6] (2) in the trigonal crystals (ORTEP, 50% probability ellipsoids except for fluorine atoms, hydrogen atoms omitted). The projection follows the C2 axis passing through the center of the macrocycle.
Figure 5. Complete structure of complex 2 (ORTEP, 50% probability ellipsoids except for phenyl carbon atoms and fluorine atoms, hydrogen atoms omitted).
contacts (Figure 5). Phosphine sulfide coordination to silver(I) atoms has been observed previously,24-26 but no µ3coordination has been reported.
Figure 3. Twisted boat form of the central metallacycle of compound 2 (point group C2 symmetry). The interatomic distances are Ag1-Ag2 ) 2.9133(6) Å, Ag2-Ag3 ) 3.0464(6) Å, and Ag3-Ag1′ ) 3.1001(6) Å.
Figure 4. Subunit [(Ph3PS)4Ag6] (ORTEP, 50% probability ellipsoids, hydrogen atoms omitted) showing the positions of the sulfur atoms above and below the metallacycle. Each silver atom is coordinated to two sulfur atoms and each sulfur atom to three silver atoms. The projection runs perpendicular to the C2 axis, which passes through the midpoint of the line connecting the atoms Ag3 and Ag3′.
tetrahedral geometry with the Ag-S and Ag-O bond lengths in broad ranges from 2.5426 to 2.8769 Å and from 2.248 to 2.326 Å, respectively, and entertain two metallophilic
It appears that the Ph3PS molecules are templates for the formation of the hexamer of silver trifluoroacetate. They provide an exposed sulfur atom which can function as a donor center for three neighboring silver centers. With the sulfur atoms capping two different silver triples, all six silver atoms can reach CN 4 with only four Ph3PS ligands, which explains the 6:4 stoichiometry. This compact array is obviously a preferred mode of organization which has the same structure regardless of the number and distribution of solvent molecules in the two different crystalline solvates. The NMR data for chloroform solutions at 20 °C indicate that the hexanuclear aggregate enjoys great fluxionality in solution, which renders the trifluoroacetate and the triphenylphosphine sulfide ligands equivalent on the NMR time scale. Cooling of samples to the solubility limit (ca. -50 °C) did not lead to line broadening or splitting of the 19F and 31P signals which are to be expected for a rigid structure with C2 symmetry. This result suggests that the Ph3PS ligands can undergo facile intra- or intermolecular “ring hopping”, meaning that they can move freely to other silver triangles with concomitant flapping of the five-membered CO2Ag2 rings. Moreover, there can be flapping of the six-membered ring of silver atoms (Figure 3). However, dissociative mechanisms also cannot be excluded. Substitution of the Ph3PS units by strong donor ligands (phosphines, isocyanides) leads to conventional complexes of other [(L)n(CF3CO2Ag]m oligomers. (24) Bembenek, E.; Crespo, O.; Gimeno, M. C.; Jones, P. G.; Laguna, A. Chem. Ber. 1994, 127, 835. (25) Livingstone, S. E. In ComprehensiVe Coordination Chemistry; Wilkinson, G., Gillard, R. D., McCleverty, J. A., Eds.; Pergamon Press: Oxford, 1987; Vol. 2, p 641. (26) Pasechnik, M. P.; Aladzheva, I. M.; Matrosov, E. I.; Pisarevski, A. P.; Struchkov, Y. T.; Mastryukova, T. A.; Kabachnik, M. I. IzV. Akad. Nauk SSSR, Ser. Khim. 1994, 708; Russ. Chem. Bull. 1994, 43, 660.
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Djordjevic et al. Table 1. Crystal Data, Data Collection, and Structure Refinement Details for {(Ph3PS)4‚[AgOC(O)CF3]6}‚(CHCl3)0.87 (2)
2CH2NCAgOC(O)CF3]2
(1), {(Ph3PS)4‚[AgOC(O)CF3]6} (2), and
[pTolSO2CH2NCAgOC(O)CF3]2 (1)
{(Ph3PS)4‚[AgOC(O)CF3]6} (2)
{(Ph3PS)4‚[AgOC(O)CF3]6}‚(CHCl3)0.87 (2)
empirical formula
C22H18Ag2F6N2O8S2
fw cryst syst space group a/Å b/Å c/Å R/deg β/deg γ/deg V/Å3 Fcalcd/g cm-3 Z F(000) µ(Mo KR) (cm-1) T/K no. of reflns measured no. of unique reflns no. of refined params/restraints R1 [I g 2σ(I)] wR2a weighting scheme
832.24 triclinic P1h 10.9501(3) 11.2398(4) 13.8195(4) 104.2352(18) 96.633(2) 118.9642(12) 1386.14(7) 1.994 2 816 16.53 143 39342 4763 [Rint ) 0.043] 380/0 0.0297 0.0656 a ) 0.0079 b ) 2.0580 0.427/-0.331
C84H60Ag6F18O12P4S4 2502.66 trigonal R3hc 29.0992(2) 29.0992(2) 64.5822(6) 90 90 120 47359.3(6) 1.579 18 22104 13.17 143 354127 9649 [Rint ) 0.099] 636/0 0.0561 0.1146 a ) 0.0372 b ) 401.0217 0.610/-0.806
C84.87H60.87Ag6Cl2.61F18O12 P4S4 2606.61 monoclinic C2/c 53.1396(6) 15.1408(2) 27.3641(4) 90 120.4072(9) 90 18988.1(4) 1.824 8 10228 15.35 143 274446 16477 [Rint ) 0.063] 1190/0 0.0423 0.0939 a ) 0.0321 b ) 94.7621 1.090/-0.638
σfin(max/min)/e Å-3 a
[pTolSO
wR2 ) {∑[w(Fo2
-
Fc2)2]/∑[w(Fo2)2]}1/2; w ) 1/[σ2(Fo2) + (ap)2 + bp]; p ) (Fo2 + 2Fc2)/3.
Experimental Section pTolSO
Preparation of Complex 1. 2CH2NC (200 mg, 1.02 mmol) and CF3CO2Ag (226 mg, 1.02 mmol) were reacted in 10 mL of CHCl3 at room temperature in the dark overnight. The reaction mixture was evaporated to dryness in a vacuum, the residue washed with diethyl ether, and dried in a vacuum to leave 352 mg of a colorless solid (83% yield, mp 164 °C dec). Anal. Found: C, 30.92; H, 2.11. Calcd for C11H9AgF3NO4S (416.12): C, 31.75; H, 2.18. 1H NMR (CDCl3, 20 °C): δ 2.44, s, 3H, CH3; 4.76, s, 2H, CH2; 7.43 and 7.88, m, 2 × 2H, C6H4. 13C{1H} NMR: δ 21.7, s, CH3; 61.9, s, CH2; 129.2, 130.9, 132.3, and 148.1, C6H4; 163.0, br, NC. 19F NMR: δ -74.3, s. MS (FAB): m/z 498 [L2Ag]+. Preparation of Complex 2. A suspension of CF3CO2Ag (200 mg, 0.90 mmol) in 10 mL of dry CHCl3 was treated with a solution of Ph3PS (266 mg, 0.90 mmol) in another 10 mL of the same solvent at room temperature in the dark for 2 h. The solvent was subsequently removed in a vacuum, the residue extracted with pentane, and the colorless product crystallized from chloroform/ pentane and dried in a vacuum (204 mg, 54% yield, mp 167 °C dec). Anal. Found: C, 41.67; H, 2.64. Calcd for C42H30Ag3F9O6P2S2 (1251.35): C, 40.31; H, 2.42. 1H NMR (CDCl3, 20 °C): δ 7.717.43, m, Ph. 13C{1H} NMR: δ (for C1-C4, respectively) 128.6, d, J ) 88.2 Hz; 129.6, d, J ) 11.9 Hz; 132.5, d, J ) 10.4; 133.6, s. 31P{1H} NMR: δ 46.8, s. 19F NMR: δ -73.4 ppm. MS (FAB): m/z 697 [L2Ag]+. Crystals of 2‚(CHCl3)0.87 were grown from chloroform/pentane. Crystal Structure Determinations. Specimens of suitable quality and size were mounted onto the ends of quartz fibers in
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F06206R oil and used for intensity data collection on a Nonius DIP 2020 diffractometer, employing graphite-monochromated Mo KR radiation. Intensity data were corrected for absorption effects (DELABS from PLATON). The structures were solved by a combination of direct methods (SHELXS-97) and difference Fourier syntheses and refined by full-matrix least-squares calculations on F2 (SHELXL-97).27 The thermal motion of all non-hydrogen atoms was treated anisotropically. All hydrogen atoms were calculated and allowed to ride on their parent atoms with fixed isotropic contributions. During the structure refinement of both crystalline phases of the compound [(Ph3PS)4‚(CF3CO2Ag)6] (2), the atoms of two chloroform molecules were observed. While in the trigonal case none could be modeled satisfactorily, one of two solvent molecules of the monoclinic form was refined but its site found to be not fully occupied (87%). The SQUEEZE routine in PLATON was used to modify the hkl files. Further information on crystal data, data collection, and structure refinement is summarized in Table 1.
Acknowledgment. This work was generously supported by Deutsche Forschungsgemeinschaft, Fonds der Chemischen Industrie, and Heraeus GmbH. Supporting Information Available: X-ray file in CIF format. This material is available free of charge via the Internet at http://pubs.acs.org. IC048795O (27) Sheldrick, G. M. SHELXL-97, Programs for Crystal Structure Analysis, University of Go¨ttingen, Germany, 1997.
